Electrolytic process for the production of quinone and hydroquinone



Patented June 9, 1942 2,285,858 ELECTROLYTIC PROCESS FOR THE PRO-DUCTION F QUINON E QUINONE A ND unmo- Sydney Horrobin and RandalGeorgeArthur New,

- Blackley, Manchester, England, assignors to Imperial ChemicalIndustries Limited, a corpov ration of Great Britain No Drawing.

271,604. In Great Britain May 3, 1938 11 Claims. (Cl. 204-78) Thisinvention relates to the manufacture of p-benzoquinone and hydroquinone.More spe cifically it relates to the manufacture of p-benzoquinone bythe electrolytic oxidation of benzene in sulphuric acid medium, and tothe manufacture of hydroquinone by the reduction of the p-benzoquinone.In British Patent Specification No. 430,572 there is described a processforthe production of p-benzoquinone wherein benzene is passed through orstirred with an electrolyte, preferably consisting of dilute sulphuricacid or a mixture of sulphuric acid and a soluble sulphate, such assodium sulphate, and subjected to electrolysis in an electrolytic cellin which an active and stable anode of lead or an alloy of lead and aninactive cathode are disposed, preferably close to each other, theconcentration of p-benzoquinone in the cell being kept low by itscontinuous or frequent removal. In the same specification there is alsodescribed an improved process for the production of hydroquinone fromthe dilute solution of pbenzoquinone in benzene resulting from theelectrolytic oxidation, the said process comprising reducing at aboutthe boiling point of benzene and under such conditions that the benzeneis immediately distilled off and the hydroquinone obtained dissolved inwater.

The above processes have the disadvantage that there is a considerableloss of benzene due to entrainment in the gases which are evolved fromthe cell. They also have to be operated as batch processes and are notsusceptible of continuous operation.

This invention has as an object to devise a new and improved process forthe manufacture of p-benzoquinone and hydroquinone. A further object isto devise such a process which can be operated as a continuous process.A further ob. ject is to devise such a process which will avoidsubstantially all the loss of benzene associated with the knownprocesses. Further objects will appear hereinafter. These objects areaccomplished by the following invention. 7

We have now found that instead of passing the benzene through or mixingit with the electrolyte in the cell, as in the above process, thebenzene may b electrolysed entirely as a solution in dilute sulphuricacid; and that the use of such a solution has the advantage that theloss of benzene, which occurs with the above mentioned process, andwhich is due largely to the entrainment of the benzene in the gaseswhich are evolved from the cell, is entirely or almost entirely avoided.We have also found when using such a solution, that if the solutionafter flowing through the cell, has benzene passed through it, thp-benzoquinone is absorbed in the benzene and at the same time thedilute sulphuric acid is replenished with benzene and so prepared forpassing through the cell again, and consequently the process may be madea circulating one. We

have found that such a circulating process has the advantages over theabove-mentioned process, firstly that any stoppage of the process toreplenish thecell, is avoided, and secondly that agitation isunnnecessary, and consequently electrolytic cells, which are free frommoving parts, may be employed.

Our invention accordingly consists of a process for the manufacture ofp-benzoquinone by the electrolytic oxidation of benzene in solution insulphuric acid, using an anode of lead or of an alloy of lead, which hasbeen activated by the 'electrodeposition of a film of lead peroxide onits surface, and a cathode consisting of metal unaffected by theelectrolyte, characterised in that the benzene is present in theelectrolyte only as a solution in dilute sulphuric acid and that theelectrolyte is circulated through the electrolytic cell and outside thecell is brought into contact with benzene in which p-benzoquinone isabsorbed and the electrolyte replenished with benzene, the pbenzoquinone beingsubsequently removed from the benzene;

In working according to the invention the nature and preparation of theelectrodes the current density, the acid strength, and the temperatureof the electrolyte may be substantially the same as described in theabove-mentioned specification. Thus the lead alloy may consist of a hardalloy of lead containing antimony or bismuth. The temperature of theelectrolyte is conveniently 2530 C. The electrodes, however arepreferably disposed in the form of closely spaced parallel plates withsheets of cloth placed be-' tween and close to the cathodes, in such amanner that the circulating liquor flows between the cloths and theanodes.

Our invention also comprises a process for the production ofhydroquinone which comprises the reduction of the p-benzoquinoneobtained in solution in benzene as described immediately above, thereduction being effected for example, as described in theabove-mentioned specification.

The following example illustrates how the process of the invention maybe carried into effect but does not limit the invention.

r 1 Example The electrolytic cell employed contains two anodes, bothsides of each being used in electrolysis, the total anode area beingabout 17 dmF, and 4 cathodes each used on one side only. The anodes andcathodes are both of pure lead, the former consisting of plain sheetsand the latter of perforated sheets. Each anode is separated from eachof the adjacent cathodes by /2 inch sheets of woollen cloth bein fixedbetween close to the surface of the cathode. linlets and outlets for theelectrolyte are provided at the bottom of the cell, which is so arrangedthat the acid flows consecutively over each of the 4 anode surfaces. Thecathodic hydrogen passes through holes in the cathode to a compartmentat the back isolated from the rest of the cell. 7

To activate the anodes the cell is filled with a 10% solution ofsulphuric acid, and a current of 40 amps. passed with the anodespositive. As soon as the voltage is seen to rise rapidly the current isreversed. This procedure is carried on for about 1 hour, and a steadycurrent of 40 amps. is then passed, with the anodes positive, for afurther hour. In this way an active surface is produced on the anodes.The cell is then ready for use.

10% sulphuric acid containing dissolved benzene is now circulated at therate of 30 litres per hour through the cell, down a glass column andback through the cell, continuously. The temperature of the acid is25-30" C. and a current of 40 amps. corresponding to an anode currentdensity of 2.4 amps./dm. is passed through the cell. The glass column,185 cms. long and ofinternal diameter 5.5 cms. is packed with inchunglazed porcelain rings. Benzene from a reservoir rises up the glasscolumn at a rate of to 1 litre per hour thus meeting and interminglingwith the sulphuric acid which has come from the cell and extractingtherefrom the quinone, which is then reduced to hydroquinone by iron andacid as described in British Specification No. 430,572.

The cell is kept in continuous operation until the acid becomes fouledwith oxidation products of benzene which dissolve in the electrolyte.The electrolyte is then discarded, the acid renewed, and the cell putinto operation again after the anodes have been activated as alreadydescribed.

As many apparently widely different embodimentsof this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific embodimentsthereof except as defined in the appended claims.

We claim:

1. A process for the manufacture of p-benzoquinone which comprisessubjecting a solution of benzene in an electrolyte to electrolyticoxidation in a cell forming p-benzoquinone, withdrawing from said cellelectrolyte containing p-benzoquinone, passing said electrolyte outsidesaid cell in contact with additional benzene thereby extracting saidp-benzoquinone and replenishing said electrolyte with benzene, removingbenzene containing the extracted p-benzoquinone from contact with saidelectrolyte, and returning to said cell the electrolyte containingbenzene abscrbed from the aforesaid contact.

2. A process for the manufacture of p-benzoquinone which comprisessubjecting a solution of benzene in dilute sulphuric acid toelectrolytic oxidation in a cell forming p-benzoquinone, withdrawingfrom said cell dilute sulphuric acid conquinone, passing saidelectrolyte outside said cell lit in counter-current contact withadditional benzene thereby extracting said p-benzoquinone andreplenishing said electrolyte with benzene, removing benzene containinthe extracted p-benzoquinone from contact with said electrolyte, andreturning to said cell the electrolyte containing benzene absorbed fromthe aforesaid contact.

l. In a process for the manufacture of hydroquinone by reduction ofp-benzoquinone, the steps which comprise subjecting a solution ofbenzene in an electrolyte to. electrolytic oxidation in a cell formingp-benzoquinone, withdrawing from said cell electrolyte containingpbenzoquinone, passing said electrolyte outside said cell in contactwith fresh benzene thereby extracting said p-benzoquinone, forming asolution thereof in said fresh benzene and replenishing said electrolytewith benzene, removing fresh. benzene containing the extractedp-benzoqui- I none entirely in solution from contact with saidelectrolyte for reduction of the p-benzoquinone entirely in solution insaid fresh benzene to hydroquinone, and subjecting benzene absorbed inthe electrolyte from said contact step to electrolytic oxidation asaforesaid.

5. A continuous process for the manufacture of p-benzoquinone whichcomprises subjecting benzene entirely in solution in a diluteelectrolyte to electrolytic oxidation in a cell forming p-benzoquinone,characterized in that only such amount of benzene is present in saidelectrolyte as can be maintained entirely in solution therein,withdrawing from the cell during said process electrolyte containingp-benzoquinone, removing from said electrolyte outside said cellp-benzoquinone, contacting a dilute electrolyte outside said cell withfresh benzene forming a solution thereof in said electrolyte andintroducing to the cell during said process said electrolyte containingbenzene entirely in solution.

6. A continuous process for the manufacture of p-benzoquinone whichcomprises subjectingbenzene entirely in solution in dilute sulphuricacid to electrolytic oxidation in a cell forming 'p-benzoquinone,characterized in that only such electrolytic oxidation in'a cell forming'p-benzoquinone, characterized in that only such amount of benzene ispresent in said electrolyte as can be maintained entirely in solutiontherein, withdrawing from the cell during said process electrolytecontaining p-benzoquinone, removing from said electrolyte outside saidcell p-benzoquinone, contacting said electrolyte with fresh benzeneforming a solution thereof in said electrolyte and recycling to the cellduring said process said electrolyte containing benzene entirely insolution.

8. A continuous process for the manufacture of p-benzoquinone whichcomprises subjecting benzene entirely in solution in dilute sulphuricacid to electrolytic oxidation in a cell forming p-benzoquinone,characterized in that only such amount of benzene is present in saiddilute sulphuric acid as can be maintained entirely in solution therein,withdrawing from the cell during said process dilute sulphuric acidcontaining p-benzoquinone, removing from said dilute sulphuric acidoutside said cell p-benzoquinone, contacting said dilute sulphuric acidwith fresh benzene forming a solution thereof in said dilute sulphuricacid and recycling to the cell during said process said dilute sulphuricacid containing benzene entirely in solution.

9. In a process for the manufacture of hydroquinone by reduction ofp-benzoquinone, the steps which comprise subjecting a solution ofbenzene in dilute sulphuric acid to electrolytic oxidation in a cellforming p-benzoquinone, withdrawing from said cell dilute sulphuric'acidcontaining p-benzoquinone, passing said dilute sulphuric acid outsidesaid cell in contact with fresh benzene thereby extracting saidp-benzoquinone, forming a solution thereof in said fresh benzene andreplenishing said dilute sulphuric acid with benzene, removing freshbenzene containing the extracted p-benzoquinone entirely in solutionfrom contact with said dilute sulphuric acid for reduction of thep-benzoquinone entirely in solution in said fresh benzene tohydroquinone, and subjecting benzene absorbed in the dilute sulphuricacid from said contact step to electrolytic oxidation as aforesaid.

10. A process for the manufacture of p-benzoquinone which comprisessubjecting benzene entirely in solution in a dilute electrolyte toelectrolytic oxidation in a cell forming 'p-benzoquinone,withdrawingfrom said cell electrolyte containing p-benzoquinone, passing saidelectrolyte outside said cell in contact with additional benzene therebyextracting said p-benzoquinone and replenishing said electrolyte withbenzene, removing benzene containing the extracted p-benzoquinone fromcontactwith said electrolyte, and subjecting benzene absorbed in theelectrolyte from said contact to electrolytic oxidation as aforesaid.

11. A process for the manufacture of p-benzo- I quinone which comprisessubjecting benzene endilute sulphuric acid from said contact toelectrolytic oxidation as aforesaid.

SYDNEY HORROBIN. RANDAL GEORGE ARTHUR NEW.

